Zinc Carbonate Ore Conversion Process

The conversion of zinc carbonate ore (ZnCO$_3$) into zinc oxide (ZnO) is a necessary step before the metal can be extracted via reduction.

Understanding Calcination

This process is called calcination. It involves heating the ore strongly in a controlled environment.

The chemical reaction is the thermal decomposition of zinc carbonate:

$ \text{ZnCO}_3\text{(s)} \xrightarrow{\Delta, \text{ limited air}} \text{ZnO}\text{(s)} + \text{CO}_2\text{(g)} $

• The heating provides energy for the decomposition.
• Limited air is used to prevent unwanted side reactions, such as the oxidation of ZnO to zinc sulfate (ZnSO$_4$) if sulfur impurities are present, or further oxidation of the product. It mainly helps in driving off the CO$_2$ gas and any volatile impurities.

Evaluating Other Options

• Heating with aluminium powder or Heating with carbon powder: These methods involve reduction, which occurs *after* the zinc oxide has been formed, not during the conversion of carbonate to oxide. Carbon powder is used in the subsequent reduction step (smelting).
• Heating strongly in excess air: While heating occurs, excess air can potentially lead to the formation of undesirable zinc sulfate, making calcination in limited or controlled air preferable.

Therefore, heating strongly in limited air is the correct method for calcination.